non-vacuous-verification

A testing rule requiring every check to be capable of failing when the defect is present. A green result is meaningful only when the test or verifier could have produced a failure.

In plain words
What is it for?
Use it when writing regression tests, verification scripts, type tests, or checks for generated files. First demonstrate that the check fails for the broken case, then confirm it passes after the fix.
Why use it?
It prevents false confidence from tests that pass both before and after a fix. It also exposes empty inputs, broken type fixtures, and untested generated-code paths.

Cursor rule for Codex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/prisma/orm/non-vacuous-verification
Clone the repo
git clone --depth 1 https://github.com/prisma/orm

Made for: Codex.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 342 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00000 $0.00342
Opus 5 $0.00000 $0.00171
Sonnet 5 $0.00000 $0.00068
Haiku 4.5 $0.00000 $0.00034

Measured 2d ago against content hash 17c711dcf096, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

non-vacuous-verification scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.agents/rules/non-vacuous-verification.mdc · 21 lines

What it actually says

Non-vacuous verification

A verification that cannot fail converts absence of evidence into false confidence. Before trusting a green result, name what would have made it red.

  • A regression test must be red before the fix — run it against the unfixed code and record the failure. If the triggering scenario cannot be reproduced (e.g. a transport race), don't ship a test that is green in both worlds: make the seam testable and test the seam directly.
  • A verifier must fail (or loudly warn) on empty input. "All 0 known cases verified" is a discovery failure, not a pass.
  • Guard type tests against any poisoning. skipLibCheck + an unresolvable import in a fixture .d.ts makes every dependent assertion vacuous (T & any is any). Add a not.toBeAny() sentinel on the fixture's central types.
  • Comments are not evidence. A comment describing a guard does not mean it exists — read the code it claims to describe; correct the comment when it lies.
  • Generated files: test claims by regenerating. Reading the generator is not evidence; running it is.
  • Instrument before designing a fix for a hard-to-reproduce failure — a counter proving "this catch never runs" kills a wrong hypothesis in one run.
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 21 lines · 0 tokens per session scan A 17c711dcf096

Subscribe to this mod's changes

non-vacuous-verification is a cursor rule published in the GitHub repository prisma/orm (47,587 stars, last pushed today), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 342 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.